Enhanced sludge dewaterability and confined antibiotics degradation in biochar-mediated chemical conditioning through modulating Fe oxidative states distribution and reaction sites in multiphase

Abstract

For antibiotic-enriched waste activated sludge, classical iron-based chemical conditioning significantly enhanced sludge dewaterability. Nevertheless, the intricate constituents within sludge rapidly depleted reactive oxygen species (ROS), leading to challenges such as excessive production of iron sludge and inadequate elimination of antibiotics from sludge. Herein, we proposed an innovative strategy integrating biochar with Fe(II) for peroxymonosulfate (PMS) activation, aiming to enhance both sludge dewaterability and antibiotics elimination simultaneously. Compared to classical chemical conditioning of Fe(II)/PMS, the presence of biochar not only reduced bound water content of sludge from 1.36 g/g DS to 0.97 g/g DS, but also enhanced sulfamethoxazole (SMX) degradation rate constant from 0.015 min^-1 to 0.042 min^-1. Mechanism studies disclosed the essential roles of biochar in modulating Fe oxidative states distribution and reaction sites in multiphase. Initially, biochar elevated Fe(II)/Fe(III) ratio from 0.38 to 0.78 by abundant carbon defects, which significantly promoted the cumulative concentration of predominant ROS, hydroxyl radicals (•OH), from 4.6 mM to 8.1 mM. Subsequently, EPS underwent destruction by •OH, leading to the liberation of antibiotics and negatively charged polysaccharides (PS), proteins (PN). Secondly, biochar enriched hydrophobic PN with an elevated ratio of PN/PS from 0.92 to 1.50, while the charge neutralization occurred between Fe(II)/Fe(III) and PN, PS, leading to sludge particles granulation. Finally, the mesoporous structure of biochar not only achieved SMX enrichment, but also enhanced the mass transfer of Fe(II)/Fe(III) from sludge aqueous phase to its surface, ensuring that the in-situ generated •OH efficiently targets the locally concentrated SMX. Overall, this work provides a new guidance for developing biochar-mediated chemical conditioning, aiming to enhance the generation and utilization of •OH for antibiotics elimination from sludge.